I. Field of the Invention
This invention relates to a method and apparatus for enhancing images of transilluminated materials wherein the area within the image containing the information of interest is the result of differential absorption of the transmittal energy and/or exhibits low contrast. This invention also relates to a transillumination method and apparatus for the diagnosis of breast tumors and other breast lesions using nonionizing radiation energy such as light or sound. More particularly, this invention relates to a method and apparatus for digitally enhancing localized areas of interest in the resulting image of a breast to aid in the diagnosis of malignant tumors, cysts and other lesions. As used herein, transillumination is intended to cover the transmission of both light and sound through an object or material at the appropriate wavelength transmission range (window). Although light and sound are the known non-ionizing forms of radiation, the image enhancement processes described herein may be applicable to electronic images resulting from other forms of transillumination.
II. Description of the Prior Art
Transillumination of the breast with light to assist in the detection and diagnosis of malignant tumors is known. Generally, the technique involves passing light in approximately the 600-1000 nanometer wavelength range through the breast, and directly examining the breast or a recorded image of the breast for the presence of lesions. The lesion may be observed because the human breast comprises fat, fibrous tissue and blood vessels. Cancerous lesions of interest are filled with and surrounded by blood which strongly absorbs light in the selected wavelength range. Moreover, such lesions absorb the light more strongly than the breast's blood vessels. Thus, malignant tumors may be detected because they are more optically dense than the remainder of the breast tissue.
A major advantage of using light is the avoidance of ionizing radiation such as X-rays. This advantage is also applicable to other forms of nonionizing radiation energy such as ultrasound. Although not as useful in imaging cancerous breast lesions, ultrasound does generate images of some lesions such as cysts as a result of differential absorption, and therefore the present invention is applicable to those images.
Optical and electro-optical apparatus have been developed to aid in using the transillumination technique. These apparatus have incorporated improvements in the light source, photographic imaging and the use of television cameras and monitors. Moreover, television cameras have been coupled with analog and digital image enhancement processes to aid the medical practitioner in identifying lesions of interest, particularly cancerous tumors.
Notwithstanding the substantial interest in the transillumination of non-ionizing electromagnetic radiation for diagnosis of breast lesions, the technique has not met with general acceptance among medical practitioners. Although the specific reasons for the technique's lack of acceptance are many and varied, in general it has not been accepted as a clinically reliable substitute or adjunct to X-ray mammography. The principal problem appears to be the technique's inability to detect lesions unless they are close to the breast surface or there is otherwise a large contrast between the lesion and the remainder of the image.
Transillumination of the female breast for diagnostic purposes was proposed at least as long ago as 1928, and reports of the clinical use of a high intensity light source to illuminate the interior of a breast date back to 1929. The procedure was abandoned because it had only a limited ability to distinguish benign and malignant tumors.
The procedure was resurrected in the 1970s when a water cooled high intensity light source to improve illumination was combined with a photographic camera which recorded black and white and infrared images. The apparatus proved to be bulky and the actual examination required long exposure times in a completely dark examination room.
Improvements continued. In 1979, a small hand-held device called a "diaphanoscope" was introduced. This unit contained a broad spectrum light source, fiber optics and a fan that air-cooled the system. Images of the illuminated breast were photographically recorded. Reports of clinical use of the diaphanoscope indicate that abnormal breast tissue absorb light differently than normal tissue, and photographs of transilluminated breast were considered to be good but did not add any new or significant data to breast examination that could not be obtained with X-rays or palpation. It was however determined that transillumination effectively illuminated the more dense breasts of younger women.
Subsequently, infrared light detecting cameras and highly sensitive television cameras and monitors were used to obtain a real-time image that the medical practitioner could view during an examination. Images could be stored, compared to the other breast and photographed using a Poloraid or 35 mm camera attached to the monitor.
Still other work involved the use of flash exposure and color photographs taken with infrared sensitive film.
This work was followed by the digitization of breast images, storage and, to a limited degree, processing of the stored information. Also "false color" was incorporated to give enhanced differentiation to the images. Spectrascan, Inc. of South Windsor, Conn., USA offers a commercial embodiment of a breast illumination system incorporating the use of a video camera, digitization of the breast image, algorithmic image reconstruction, amplification, and display in black-and-white on a video monitor. (See U.S. Pat. Nos. 4,467,812 and 4,485,949 which relate to the Spectrascan, Inc. transillumination method and apparatus.)
More recent apparatus have incorporated freeze frame capability to permit a stable image for photography and/or digitization. The apparatus is also provided with the capability to digitally record and retrieve the images.
Approximately 25 clinical studies using a wide range of patient populations, diagnostic imaging techniques and clinical exams have been done. In general, these studies show that electromagnetic transillumination (also referred to as light scanning) has promise as a breast examination system separate from palpation, X-ray mammography and ultrasound. However, the results of the studies do not correlate sufficiently to permit widespread acceptance of light scanning as a diagnostic technique. One study concluded that X-ray mammography is far superior to light scanning. However, another study concluded that infrared light scanning of the breast is effective in the hands of trained personnel and it should be used as an adjunct to routine breast examination or X-ray mammography to increase the detection of breast pathology.
A clinical study comparing transillumination light scanning using a Spectrascan Light Scan Model 10, and screen-film mammography of the breast was made in 1987. The authors of the study concluded that transillumination light scanning is not competitive with X-ray mammography as a screening method for breast cancer detection. Furthermore, they were unable to identify a select subpopulation of women who might benefit from light scanning as an adjunct to X-ray mammography.
A study conducted a year earlier, also involving the Spectrascan Light Scanner, suggested that X-ray mammography was superior for detecting malignancy.
Notwithstanding the foregoing, the clinical studies suggest that light scanning has an adjunctive value; that is, by using X-ray mammography and light scanning side by side, the overall reliability of imaging for breast disease may be improved.
Several important points may be derived from the conclusions of the light scanning clinical studies. These include:
1. Light scanning is effective even though the currently available equipment is not nearly so sophisticated as X-ray and ultrasound equipment.
2. Light scanning is safer than X-ray mammography because there is no ionizing radiation.
3. Light scanning is highly complimentary to X-ray mammography rather than being a competitive imaging system.
4. Light scanning suffers somewhat because medical practitioners are not familiar with light scanning procedures.
5. Light scanning has particular applicability as a screening procedure for women between the ages of 30 and 40 who would otherwise receive a X-ray mammogram every two years and women over the age of 40 who should have a mammogram every year but do not want X-ray exposure. Light scanning has particular value as an adjunctive diagnostic tool for yearly breast examination in women under the age of 30, high risk patients and cancer patients.
Clinical studies aside, particular problems with existing light scanning apparatus include inability to clearly perceive deep lesions and tumors located near the chest wall. Existing apparatus have difficulty in detecting minimal, non-palable tumors and also produce poor results for patients with clinically occult malignancies. Still further, existing light scan apparatus have not been useful in recent biopsy, aspiration, trauma or hemorrhage patients because of the presence of light absorbent hemoglobin. Significant to the invention described herein, prior light scanning apparatus lacks sensitivity in cyst detection relative to ultrasound.
There therefore is a need for a more sensitive process and apparatus for transillumination diagnosis of breast lesions using non-ionizing radiation (e.g. light scanning or sound) to generate a clinically useful image. It is particularly desirable that such process, and the apparatus for carrying out the process, be more sensitive to the detection of occult, non-palpable breast cancer.